Second-century case of semi-identical twins identified

(Newser) – There are identical twins, there are non-identical twins – and in incredibly rare cases, there are twins who fall somewhere between the two. The second case ever recorded of semi-identical or sesquizygous twins has been described in a recently published study published in the New England Journal of Medicine . The twins, born in Brisbane, Australia in 2014, were the first of their kind to be identified during pregnancy. Professor Nicholas Fisk, who was in charge of caring for the mother and twins, explained how this happened, the BBC reported. "The mother's ultrasound at six weeks showed a single placenta and positioning of amniotic bags, which indicated she was expecting identical twins." However, an ultrasound at 14 weeks showed that the twins were male and female. is not possible for identical twins. "

With identical twins, divide a fertilized egg into two; Brotherly twins are the result of two eggs being fertilized by two sperms. Sesquizygotic twins occur when an egg is fertilized by two sperms before being split off. That means there are three sets of chromosomes – two from the father and one from the mother – and experts say it is very unusual for such embryos to survive, Science Daily reports. The twins have more in common with each other, genetically than brotherly twins, but less than identical twins: "Genotyping of amniotic fluid from each bag has shown that the twins were maternally identical, but chimeras shared 78% of their paternal genome," the study. The other well-known case was identified in the US in 2007. (Read more twin stories.)